The objective of this study was to evaluate the effects of culture time and sex of nuclei donor cells on embryo and fetal development after nuclear transfer. Thus, bovine oocytes were matured, enucleated and reconstructed with somatic cells from an adult animal. After fusion and chemical activation, the reconstituted zygotes were cultured in Charles Rosenkranz 2 (CR2) on a granular monolayer cell at 38.8ºC in a humidified atmosphere 5% CO2 in air for seven days, and transferred to synchronized receptors. Cleavage rates and development to blastocyst of embryo reconstructed with cells cultured for a longer time were lower than rates obtained with other culture times. Moreover, these produced blastocysts did not result in the development of full term pregnancy. Although cleavage rates were higher in female embryos, the number of embryos that reached blastocyst stage was higher in male embryos. During gestation period, females showed higher abortion rates from 90 to 120 days of gestation. These results indicate that cells donnors of nuclei cultured for long periods make the production of blastocysts difficult and increase the chances of losses during pregnancy. Cloned male embryos are more succesful in becoming blastocysts and result in lower gestational loss rate.
bovine; cell passage; fibroblast; nuclear transfer; sex
